Processes such as gel filtration, ion exchange chromatography, and affinity chromatography are known for the separation of complex mixtures of nucleic acids, enzymes, or other biopolymers. Whereas only crude classification, that is, separation according to molecule size or molecule charge, respectively, is possible with the first two methods, a component can be selectively separated or isolated by affinity chromatography.
Requirements of this method are that the component have specific properties and that the sorbent contain a ligand specific to this component. This ligand is to be linked, if possible, with the sorbent in a covalent fashion, since bleeding out can occur if the linkage is ionic or adsorptive. The method of base pairing is as a specific selection or principle for the separation of nucleic acids. The production of sorbents for the separation of nucleic acids, which are based on the principle of base pairing, is described in the literature. J. Chromatogr. 82, 349 (1973); Nucleic Acids Res. 1, 1587 (1974).
Known carrier materials are, for example, polysaccharides or polyamides and suitable ligands are purine nucleotides, pyrimidine nucleotides and polynucleotides linked to the carrier covalently.
The aforesaid methods require several stages. First, carrier material is activated to be able to bond with the ligand. Thereafter, unreacted active centers are deactivated.
Expensive and time-consuming washing procedures are required between the individual stages. Therefore, a method is needed which links carrier to ligand covalently in a single reaction step and requires no expensive washing processes.
It has now been found in accordance with this invention, that silyl derivatives of purine and pyrimidine bases, and compounds derived therefrom, react readily and in good yields with blocked, preferably peracylated polysaccharides, in the presence of a Friedel-Crafts catalyst or of a trialkylsilyl ester, preferably a trimethylsilyl ester of a mineral acid or a strong organic acid to yield N-glycosyl derivatives.